The present invention relates to a continuous process for the manufacture of homopolymers or copolymers of ethylene.
It is known from French Pat. No. 2,202,899 to homopolymerize ethylene and to copolymerize ethylene with at least one .alpha.-olefin, continuously, in the presence of a Ziegler type catalytic system at high temperature and under high pressure.
The plant employed comprises at least one reactor comprising at least one reaction zone, at least one separator, and circuits for recycling the unreacted ethylene and, where applicable, the unreacted .alpha.-olefins (hereafter called "the monomers") towards a secondary compressor, which also receives fresh monomers from a primary compressor and which feeds the reactor at the chosen (co)polymerization pressure.
In a process of this type traces of the components of the catalytic system can be carried over with the gases circulating in the recycle circuits, causing a (co)polymerization of the recycled monomers in the circuits. (Co)polymers generally of very low molecular weight (below 2,000) are thus formed, having, under the normal conditions of temperature and pressure, the appearance of oils, greases, or waxes. Traps are generally provided in the recycle circuits to collect these (co)polymers of very low molecular weight. However, these (co)polymers can also be deposited on the inner wall of the recycle lines and their molecular weight can increase as a consequence of the continuous flow of the recycle gases containing traces of components of the catalytic system. While the polymers of very low molecular weight cause little inconvenience, being easy to remove, the (co)polymers of higher molecular weight (greater than 2,000) are a major nuisance and can cause a pressure drop in the plant, and even result in the blocking of the recycle lines.